1. Field of the Invention
This invention relates to a dielectric ceramic composition, which has purposes for a microwave frequency range, particularly a frequency range above the X-band and has a high dielectric constant, a high unloaded Q and stable temperature characteristics in such high frequency ranges.
2. Description of the Prior Art
With recent development of communication networks the operating frequency range is increased up to the microwave range. In this connection, a dielectric ceramic is finding such applications as impedance matching in dielectric resonators, microwave integrated circuit substrates and various microwave circuits in the microwave frequency range. Particularly, its demand is recently increasing for the purposes of frequency stabilization of filters, guns and FET microwave oscillators. In the meantime, there is a recent trend for smaller sizes of microwave circuits. The size of the microwave circuit depends on the wavelength of a propagating electromagnetic wave. The wavelength of the electromagnetic wave propagating through a microwave circuit utilizing a dielectric is given as .lambda..sub.0 /.sqroot..epsilon. where .lambda..sub.0 is the wavelength of the wave propagating through vacuum and .epsilon. is the relative dielectric constant. This means that the higher .epsilon. is, the smaller circuit element can be realized. For this reason, there is a strong demand for a dielectric ceramic composition, which causes low loss, has stable temperature characteristics and has a high dielectric constant.
Prior art dielectric ceramic materials include ZrO.sub.2 -SnO.sub.2 -TiO.sub.2, BaO-TiO.sub.2, partly substituted for by different elements, dielectric ceramic having positive temperature coefficient of the relative dielectric constant and mixtures of glass and TiO.sub.2, with the temperature coefficient of the relative dielectric constant thereof being negative, for providing controlled temperature coefficients of the relative dielectric constant. These materials, however, have various problems, e.g., low relative dielectric constant, low unloaded Q and incapability of providing a desired temperature coefficient.